An ink jet printer that attaches ink droplets onto a medium, such as paper, and forms an image or characters is known. The ink jet printer is provided with an ink jet head that discharges ink droplets in accordance with an image signal.
The ink jet head is provided with a nozzle that discharges ink droplets, an ink pressure chamber that is in communication with the nozzle, and a pressure generation element that generates pressure to discharge an ink in the pressure chamber from the nozzle. A piezoelectric body is used as the pressure generation element. A piezoelectric element that is operated by the piezoelectric body is an electromechanical element that converts a voltage into a force. A voltage applied to this piezoelectric element causes contraction, decompression, or shear deformation. Pressure is generated in the ink in the pressure chamber by means of deformation of the piezoelectric element. Lead zirconate titanate (PZT) is used for representative piezoelectric elements. An inkjet head of the related art includes a substrate, in which an ink pressure chamber is formed, a diaphragm, which is stacked on the substrate, and a piezoelectric element, which is made on the diaphragm. A thin-film piezoelectric body tends to deteriorate when a high voltage is continuously applied for a long period of time. The deterioration of the piezoelectric body shortens the life of the ink jet head.